Since you claim not be familiar with the ERC20 and myetherwallet. I think what you need to know is that Myetherwallet is a web wallet and every web wallet are vulnerable to attack so i will advise you to integrate
1) the metamask extension on your browser import your ETH wallet on metamask using your private keys.
2) Googling the token online to find the exchange where it listed (example google "
datum token" which is listed on capital market and huobi is the best exchange for you to sell it).
Note : you need to consider the price of the token, tx fee and exchange withdraw limit if the token is not listed on instant exchange like uniswap so it wont be a waste of time, efforr and tx fee from your ending
- Go to uniswap
- connect wallet
It not all ERC20 that are traded on uniswap and is not advisable for the OP to connect with uniswap using Myetherwallet.